1. Field of the Invention
The present invention relates to a motor drive apparatus configured to cause a steeping motor to drive a driven member and an optical apparatus such as an image pickup apparatus which includes the motor drive apparatus.
2. Description of the Related Art
A lot of optical apparatuses including a movable driven member such as an optical element or an image sensor and using a stepping motor as a driving source for driving the driven member are conventionally provided. The stepping motor rotates by an angle corresponding to the number of pulse signals supplied thereto to hold its stop position, so that drive of the stepping motor is generally controlled by simple open-loop control that only counts the number of the pulse signals supplied to the stepping motor.
However, in the open-loop control, detent torque that is load torque unique to the stepping motor or variation of movement load (load variation) that is generated during movement of the driven member deteriorates stop position accuracy of the stepping motor. Such deterioration of the stop position accuracy leads to deterioration of positional control accuracy of a focusing lens as the driven member in zooming or focusing, that is, deterioration of focusing performance.
Japanese Patent Laid-Open No. 2001-178193 discloses a closed-loop control method that provides, to a stepping motor, a sensor for detecting rotational angle of the stepping motor, and that performs feedback control so as to coincide an actual rotational angle of the stepping motor detected by the sensor with an instruction rotational angle therefor output from an instruction circuit.
However, the closed-loop control method for the stepping motor disclosed in Japanese Patent Laid-Open No. 2001-178193 does not consider the deterioration of the stop position accuracy due to the load variation in a case of installing the stepping motor to an actual optical apparatus and using the motor for driving the driven member.